I upped the voltage, essentially no useful change. I switched to a different stepper with more torque, and got some more torque. That was a positive improvement. Then I switched to an UNO R3 with a GRBL board and external stepper drives with 48v power supplies. That made a much bigger difference. Strangely, also ran significantly quieter which I didn’t expect. Better acceleration (enough to break belts), gobs or torque. Switched to kevlar belts and thats not a problem any more. I just got a SuperGerbil board, working to set that up now. I’m spectacularly unhappy with the keyestudio grbl board, and when I started looking for a replacement I got distracted…supergerbil seems to have a whole lot of activity, which grbl doesn’t, requires different hardware but can be run by any grbl compatible sender and it got my attention more than a better grbl shield for the UNO.